Caries is a process caused by bacteria that leads to the destruction of dental tissues and can result in tooth loss if not treated in due time. The demineralization of dental tissues (enamel, dentin or cement) is caused by acids produced by bacterial fermentation of food residues in the diet, especially sugars. The presence of the acids lowers the pH and causes the dissolution of enamel and transport of calcium and phosphate into the oral environment.
Once installed, the evolution of caries can be divided into three phases. In the first phase, the caries affects only the enamel; in a second phase, it deepens and enters the dentin; in the third stage, it reaches the root channel. In the second, and especially in the third phase, toothache starts caused mainly by inflammation due to bacterial aggression.
In order to prevent the carious process and restore the tooth's normal function, various techniques and procedures that make use of different materials are used in the treatment of caries. After the diagnosis of caries, the first step is the partial or total removal of carious tissue followed by the steps of pulp protection (artery, veins and nerves) and definitive restoration of tooth. For tooth restoration, basically two materials are used. The first material, used internally (intermediate restorative material), has biological properties that protect the pulp. The second material, used externally, restores the outer shape of the tooth and is called definitive restorative material. The protection of the pulp with intermediate restorative material, prior to the final restorative material, is needed because definitive restorative materials do not have the necessary biological properties required to protect the pulp and in fact are usually aggressive to the pulp. Desirably these intermediate materials have the ability to create an unsuitable environment for bacterial growth, and additionally induce the repair of the pulp and the remaining dentin.
Nevertheless, when there is a delay in seeking treatment, to the point that the carious process invades the radicular channel and bacteria cause the destruction of the arteries, veins and nerves, it is necessary to undergo root channel treatment. This treatment is performed in three stages: removal of dental pulp, debridement of the channel walls to remove the bacteria adhered thereto, and finally filling the channel with a filling material. It is highly desirable that this filling material is able to promote an efficient sealing of the root channel and preferably that it also acts as an antibacterial and promotes remineralization.
The common products used as protectors of the dental pulp (artery, veins and nerves) as intermediate material prior to definitive restoration or as channel filling materials contain calcium hydroxide in their formulations. Calcium hydroxide has three important properties for dental treatment. Firstly, calcium hydroxide is capable of neutralizing the acidic components (that dissolve dental tissues) produced by bacteria. Secondly, calcium hydroxide makes the environment unsuitable for bacterial growth (making it highly alkaline). Finally, calcium hydroxide induces the formation of dentin and bone, recovering the regions damaged by acids from bacteria. However, calcium hydroxide has a high solubility in slightly wet environments, which makes its use as a calcium ion source disadvantageous in cases where product stability over time is required.
Over the years several formulations based on calcium hydroxide have been used to treat dental cavities caused by caries. Formulations are usually aqueous or in the form of pastes, which means that although they have the ability to release calcium, they are not adequately resistant to withstand the compression of the definitive restorative material and the masticatory load.
The first report of a cement with properties similar to the present invention, that is, the ability to release calcium and good mechanical strength was made by Wheeler in the U.S. Pat. No. 2,516,438. This document describes compositions presented in a powder/liquid form, wherein the powder consists mainly of calcium hydroxide and the liquid of eugenol. According to the author, the composition would be a suitable capping material for the pulp. However, this invention occurred before the onset of restorative materials based on methacrylates, which polymerize in the presence of free radicals. Since it is widely known that eugenol has the ability to inhibit the radical polymerization of these resin materials, the use of eugenol combined with restorative materials based on methacrylates, is thus currently contraindicated. Additionally, the invention described in U.S. Pat. No. 2,516,438 uses calcium hydroxide as a calcium source, that, as previously described, has an excessive solubility, affecting the integrity of the material over time.
In an attempt to overcome the deficiencies of the aqueous compositions or compositions containing organic solvents (for example, eugenol), U.S. Pat. No. 3,047,408 relates to a composition containing a mixture of calcium hydroxide in excess with a polyhydric alcohol and salicylic acid esters in a powder/liquid form. This mixture reacts to form a permeable and rigid mass of calcium phenolate, having free calcium hydroxide dispersed therein. With this composition, a material with calcium ion release capacity, without the disadvantageous need of using eugenol, was obtained. However, the invention still has the limitation of having calcium hydroxide as a calcium source, compromising the material's performance over time due to its high solubility in humid environments.
U.S. Pat. No. 4,240,832 relates to a composition in a paste-paste form, based on calcium hydroxide and a salicylic acid ester based resin. Despite the advantageous paste-paste presentation, the salicylate resin used (or salicylic acid ester resin) is the condensation product of methyl salicylate with paraformaldehyde, which presents serious environmental and occupational risks during their production.
Subsequently, U.S. Pat. No. 5,922,785 also relates to a composition in a paste-paste form, based on calcium hydroxide and salicylate resin. Advantageously, said invention does not use aldehydes in the synthesis of salicylate resin, making the process safer. However, it still has the disadvantage of using calcium hydroxide as a calcium ion source.
U.S. Pat. No. 5,415,547 also relates to a repair material for dental structures which is able to release calcium ions based on Portland cement. Despite using a more suitable calcium source, the adherence of the cement depend on its mixture with water, resulting in a material with very weak mechanical properties, and having only indication limited in situations where there is no requirement for mechanical strength during its use.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.